SUMMARY Fission yeast cells utilize Arp2/3 complex and formin to assemble diverse filamentous actin (F-actin) networks within a common cytoplasm for endocytosis, division and polarization. Although these homeostatic F-actin networks are usually investigated separately, competition for a limited pool of actin monomers (G-actin) helps regulate their size and density. However, the mechanism by which G-actin is correctly distributed between rival F-actin networks is not clear. Using a combination of cell biological approaches and in vitro reconstitution of competition between actin assembly factors, we discovered that the small G-actin binding protein profilin directly inhibits Arp2/3 complex-mediated actin assembly. Profilin is therefore required for formin to compete effectively with excess Arp2/3 complex for limited G-actin, and to assemble F-actin for contractile ring formation in dividing cells.

Dilution with physiologic saline solution and other fluids accelerates the coagulation of properly collected normal and hemophilic blood and plasma in silicone coated vessels, with or without the aid of activating agents such as platelets, thromboplastin, cephalin, glass particles or plasma euglobulin fractions. When normal plasma is diluted under a concentration of about 20 per cent, its rate of clotting is prolonged, principally because of diminution in prothrombin. Regardless of the activating agent used, the rate of coagulation of hemophilic plasma can be made equal to that of normal plasma by appropriate dilution. These findings speak against the existence in hemophilic blood or plasma of a deficiency in any procoagulant factor, and support the concept of the presence in excess of a stabilizing inhibitor which slows the conversion of prothrombin to thrombin by one or both of the following mechanisms: (1) reducing or inactivating the effect of released coagulants (antithromboplastin activity) (2) conjugation with a procoagulant thereby maintaining it in an inactive form (anti Ac-globulin activity).

Substance use continues to be closely associated with both HIV infection and treatment considerations in all at-risk populations. Among those groups heretofore not well characterized epidemiologically or clinically are those dual-risk men who have sex with other men (MSM) and use and/or inject drugs. Of particular current concern with regard to drug-using MSM is the growth in popularity of a group of recreational or so-called party drugs associated with specific social and sexual environments and networks. Chief among these drugs are hallucinogens, such as MDMA, ketamine, and GHB, and stimulants, such as cocaine, amphetamines, and methamphetamine. Increased methamphetamine use by MSM is particularly alarming because of its reported associations with high-risk injecting and sexual behaviors. Preliminary data are reported from an ethnographic exploration of MSM methamphetamine users in the Pacific Northwest of the United States. Case studies drawn from the data illustrate the complex and variable patterns of methamphetamine use among MSM. Finally, implications for nursing are discussed, and "upstream nursing" is suggested as a means of patient advocacy for HIV nurses working with substance-using populations.

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